DIVISION OF ENVIRONMENTAL CHEMISTRY PREPRINTS OF EXTENDED ABSTRACTS: VOL. 40(2) AUGUST 2000
Temperature - fC] Sedimentation Rate - [10^ m min'Fe - [pM]
Figure 2. Measured temperature, calculated dispersion coefficient, sedimentation rates for colloidal and particulate Fe, and
predicted (lines) and experimental (symbols) distribution of Fe(ll), Felllc, Felllp in July 1995.
The temperature measured, the calculated dispersion coefficient and sedimentation rates of colloids (0.2 |jm) and particles (1
jjm), and the iron speciation calculated with the model and measured in the field are presented for one season in Fig. 2.
Generally, the model can fit experimental data quite well, suggesting that the reaction mechanisms assumed in the model can
reasonably predict the distribution of iron in the water column. Not surprisingly, it is found that the transport has an important
influence on the distribution of iron in the water column. In addition, side reactions can also explain discrepancies between
the modeled and experimental data. Although particulate lead is close to detection limit, the distribution of lead can be
reasonably modeled with the mechanism presented.
References
Baccini, P., and Joller, T. 1981. Schweiz. Zeit. Hydrol., 43,176.
Balistrieri, L.S., Murray, J.W. and Paul, B. 1994. Geochim. Cosmochim. Acta, 58, 3993.
Millero, F.J., Sotolango, S. and Izaguirre, M. 1987. Geochim. Cosmochim. Acta, 51, 793.
Mortimer, C.H. 1941. J. Ecol., 29, 280.
Pyzik, A.J. and Sommer, S.E. 1981. Geochim. Cosmochim. Acta, 45, 687.
Sigg, L. 1985. In Chemical Processes in lakes, J. Wiley, New York, p. 283.
Stumm, W. and Morgan J.J. 1981. Wiley & Sons, NY, pp. 756.
Sung, W. and Morgan, J.J, 1980. Environ. Sci. Techno!., 14, 561.
Suter, D., Siffert, C. Sulzberger, B., and Stumm, W. 1988. Natunviss., 75, 571.
Taillefert M., Rose E., and Gaillard J-F. 1997. Coli. INRA, 85, 289.
Taillefert, M., Lienemann, C-P., Gaillard, J-F., Perret, D. 2000. Geochim. Cosmochim. Acta, 64, 169.
Tessier, A. 1992. In Environmental particles, Vol. I., Lewis, Boca Raton, p.425.
Zinder, B., FurrerG. and Stumm, W. 1986. Geochim. Cosmochim. Acta, 50, 1861.
ROLE OF TRIVALENT Mn IN OXIDATION OF ORGANIC MATTER
Christopher J. Matocha and D.L. Sparks
Dept. of Agronomy, University of Kentucky, Lexington, KY 40546-0091
Dept. of Plant and Soil Sciences, University of Delaware, Newark, DE 19717-1303
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DIVISION OF ENVIRONMENTAL CHEMISTRY PREPRINTS OF EXTENDED ABSTRACTS: VOL. 40(2) AUGUST 2000
INTRODUCTION
Manganese(ll) and Mn(IV) have received the most attention in aquatic chemistry^ until recently, where solid Mn(ll) oxides and
soluble Mn(ll) complexes have been shown to be environmentally significant oxidants^'. Solid Mn(ll,IV) (hydr) oxide miner
als are powerful oxidants in soils and geochemical environments because of the vacant orbitals of sigma symmetry that
impart significant surface reactivity®. Manganese(lll) solid phases would be expected to be more kinetically reactive than
Mn(IV) minerals, however, no detailed studies have been conducted. This study was undertaken to test the hypothesis that
the lability of Mn(lll) predicted by frontier molecular orbital theory in solution affects the reductive dissolution kinetics of
naturally occurring solid Mn(lll,IV) (hydr) oxide minerals by comparing several phases with varying levels of structural Mn(lll)
in their reactivity with catechol, a model organic ligand of soil organic matter^
M AT E R I A L S A N D M E T H O D S
Reactivity studies of solid Mn(lll,IV) (hydr) oxide minerals with catechol were followed In situ using electron paramagnetic
resonance (EPR) spectroscopy and diffuse reflectance spectroscopy (DRS). Micromolar concentrations of Mn(ll)-pyrophosphate complexes were measured in the UV region at 210 and 260 nm and mM concentrations at 480 nm as described previ
ously'. Initial rates of pyrophosphate-extractable Mn(ll) from solid phase Mn minerals were used as an operationally defined
measure of available Mn(lli).
RESULTS
No correlation existed between the initial reductive dissolution rates of solid Mn(lll,IV) (hydr) oxides by catechol and surface
area or thermodynamic driving force. In contrast, the reductive dissolution rates were linearly related to initial rates of
pyrophosphate-extractable IVIn(lll), defined as available Mn(lll) (Figure 1). The positions of the Mn(lll) ligand field bands
derived from DRS analyses suggested different coordination environments for structural Mn(lll) in manganite and birnessite,
which explained the different levels of availability. Therefore, the role of Mn(lll) in different coordination environments merits
special attention In abiotic cycling of soil organic matter and Mn.
REFERENCES
1. Morgan, J.J. (1967) /n S.D. Faust and J.V. Hunter (ed.) Principles and applications of water chemistry, p. 561-626.
Wiley, New York.
2. Stone, A.T., and Morgan, J.J. (1984) Environ. Sci. Techno!. 18:450-456.
3. Kostka, J.E., Luther, G.W., III, and Nealson, K.H. (1995) Geochim.
Cosmochim. Acta 59:885-894.
4. Klewlcki, J.K., and Morgan, J.J. (1998) Environ. Sci. Techno!.
32:2916-2922.
5. Luther, G.W. Ill, Ruppel, D.T., and Burkhard, C. (1998) In D.L.
Sparks and T.J. Grundl (ed.) Mineral-water interfacial reactions:
Kinetics and mechanisms, p. 265-280. ACS Symposium Ser. No.
715, Washington, DC.
6. Luther, G.W. III. (1990) In W. Stumm (ed.) Aquatic chemical kinet
ics: Reaction rates of processes in natural water, p. 173-198.
Wiley-lnterscience, New York.
7. Evanko, C.R., and Dzombak, D.A. (1998) Environ. Sci. Technol.
32: 2846-2855.
Figure 1. Relationship between the initial rate of Mn(lll) extraction by
pyrophosphate (r) and the reductive dissolution rate by catechol (R).
THE EFFECT OF BIOLOGY ON THE pH-DEPENDENT REACTIVITIES
OF Fe AND Mn OXYHYDROXIDES IN AQUATIC ENVIRONMENTS
Ya r r o w M . N e l s o n
Dept. of Civil and Environmental Engineering, California Polytechnic State University, San Luis Obispo, CA 93407
Alyson R. Wilson and Leonard W. Lion
School of Civil and Environmental Engineering,Cornell University, Ithaca, NY 14853
Adsorption to Fe and Mn oxides has long been known to control trace metal transport in aquatic environments Qenne 1968),
but the relative magnitudes of the reactivities of these oxides in aquatic environments have been poorly understood because
of the complexity of interrelated biological and chemical factors affecting them. The relative roles of Fe and Mn oxides In
controlling trace metal adsorption were elucidated by examining the effects of biological Mn oxidation on Pb adsorption over a
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